I have problems with INNER JOIN SQL SERVER

I'm new in what data base refers .. and I'm working with the issue of INNER JOIN and the truth is that I'm not very clear about how it works and how to apply .. since I have an exercise and I can not join a third table that is related .. someone would be so kind to explain it to me .. here is an example of what I am doing .. I do not know if it is right or wrong ... since it does not give me any results ..